Composition (lean and fat tissue) of weight changes in adult Danes

Weight loss may be associated with unfavorable changes in body composition not compensated for by subsequent weight gain.

We examined the composition of weight change in relation to obesity, previous weight changes, weight-loss attempts, and physical activity.

Part of the Danish MONICA (Monitoring Trends in Cardiovascular Disease) project, this was a longitudinal population study of changes in weight and body composition, with examinations in 1982-1983, 1987-1988, and 1993-1994. A total of 1236 men and 1200 women aged 35, 45, 55, or 65 y in 1987-1988 participated. Changes in fat and fat-free mass were measured by bioelectrical impedance.

Before adjustment for age-related changes, fat-free mass made up 41% of weight lost and 24% of weight gained in men. In women, loss of fat-free mass (35%) was more than double that of gains (15%). After adjustment, the fractions of weight gained as fat-free mass were not significantly different from the fractions lost. These fractions were independent of age, obesity, and weight changes in the previous 5 y; successful weight-loss attempts; and physical activity. Independent of age and degree of obesity, weight changes were associated with greater changes in fat-free mass in men than in women.

These data do not support the theory that weight loss or weight cycling may lead to an unfavorable body composition, nor do they provide a biological explanation for why long-term weight loss is often unsuccessful. However, the metabolic and health consequences of weight change may differ in men and women.